The Smog Squad of Hong Kong Has Truckers on the Run

HONG KONG—Some workers in the central business district here like to pop out of the office for a smoke. Lincoln Chan slips out to spot smoke—the kind that pours out of old trucks.

Mr. Chan, a 41-year-old construction-industry executive, is one of Hong Kong's 5,000-plus "smoky vehicle spotters." These government-accredited citizen volunteers are charged with ridding the roads of the trucks, buses and delivery vans whose smoke-belching tailpipes make Hong Kong one of the world's smoggiest cities.